Multiple-layer immune barrier for donor cells

ABSTRACT

A system is provided, including a plurality of donor cells and a first alginate structure that encapsulates the plurality of donor cells. The first alginate structure has a guluronic acid concentration of between 64% and 74%. The system additionally includes a second alginate structure that surrounds the first alginate structure, the second alginate structure having a mannuronic acid concentration of between 52% and 60%. A selectively-permeable membrane is coupled at least in part to the second alginate structure. Other embodiments are also described.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 13/153,721, which was filed on, Jun. 6, 2011, which was filedconcurrently with PCT Patent Application PCT/IL2011/000445 on, Jun. 6,2011, both of which claim priority to U.S. Provisional Application61/351,992 filed on, Jun. 7, 2010. This application is also related toU.S. National Phase patent application Ser. No. 12/996,592, filed onJan. 13, 2011, which claims priority to PCT Patent ApplicationPCT/IL2009/000905, filed on Sep. 16, 2009, which claims priority to U.S.Provisional Patent Application 61/192,412 filed on Sep. 17, 2008, all ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

Some applications of the present invention relate in general toimplantation of donor cells in a recipient. More specifically, someapplications of the present invention relate to optimization ofimplantation of donor cells using a multiple-layer immune barrier.

BACKGROUND

Oxygen is essential to many physiological and metabolic processes,including aerobic metabolism. A lack of oxygen for implanted cells oftenleads to cell injury or death. Oxygen provision is a vital component insustaining transplanted cells.

The success of many transplants is compromised not only due tograft-host rejections, but also by ischemic conditions generated byinsufficient oxygen supply to the transplant. Following implantation ofthe cells, oxygen can be provided to the implanted cells from the bodytissue (mainly via diffusion). However, the relatively low ambientoxygen tension and the low natural diffusion rate are unable to providehighly metabolic cells with a significant, necessary amount of oxygenamount.

Islet transplantation is a clinical protocol aiming to help diabetestype I (DTI) patients. Transplanted cells, no matter their origin,elicits inflammatory and rejection reactions. To ensure engraftment andlong-term survival of transplanted islets, medical approaches to suchengraftment should target and address both (1) long-term rejectionprocesses of the host against the graft, and (2) the initialinflammatory reaction of the host against the graft.

In order to achieve stable graft function, donor tissue should beprovided with sufficient level of oxygen and should be protected fromhost immune and inflammatory cells and from their released toxicsubstances.

SUMMARY OF EMBODIMENTS

For some applications of the present invention, a multi-layerencapsulation barrier is provided which encapsulates a plurality ofdonor cells in order to protect and immunoisolate the donor cells in abody of a recipient. Typically, the donor cells comprise eitherallogeneic or xenogeneic cells of tissue or cells (e.g., functionalcells, typically, islets of Langerhans) that are transplanted andimmunoisolated by the artificial barrier. The multi-layer barriercomprises a first alginate hydrogel structure that macroencapsulates theplurality of islets and has a guluronic acid concentration of between64% and 74%. The multi-layer barrier comprises a second alginatestructure that surrounds the first alginate structure and has amannuronic acid concentration of between 52% and 60%. The multi-layerbarrier also comprises one semi-permeable membrane with pore size ofless than 0.5 microns, e.g., a Biopore™ membrane, which reduces fibrosisand prevents direct contact between donor cells and host immune cellsthus further immunoisolates the islets encapsulated in the multi-layerimmune barrier.

The multi-layer barrier is configured so as to (a) eliminatecell-to-cell contact, thereby preventing T-cell mediated cytotoxicityagainst the encapsulated tissue, (b) minimize diffusion rates of largermolecules through the layers of the barrier and toward the cellsencapsulated in the first alginate structure, and (c) provide for agreater distance for smaller molecules (i.e., cytokines and reactiveorganic substances (ROS)) to travel between cells which synthesize thesesmaller molecules and the islets that are encapsulated within the first,inner alginate structure.

The multi-layer immune barrier is formed so as to have a planar,geometric configuration, e.g., a slab, a sheet, or a disc. Typically,the multi-layer immune barrier has at least one substantially flatsurface. The first alginate structure comprises an ultrapure gradealginate with high percent of guluronic acid (i.e., MVG Pronova, Norway)and a defined composition that is cross-linked with a divalent cation(i.e., Strontium) and encapsulates the cells or tissue segments in ahydrogel. Typically, the first alginate structure houses islets atdensities of 1500-6000 islets/cm̂2 of the first alginate structure,typically, about 4000 islets/cm̂2 of the first alginate structure. Theislets are positioned in the center of the first alginate structure,i.e., the islets encapsulated by the first alginate are surrounded by athick layer of the first alginate. This central location of the isletswith respect to the first alginate layer physically isolates anddistances the islets from the surface of the multi-layer immune barrier.

Typically, the apparatus comprises a source of oxygen, or an oxygensupply (e.g., a vessel comprising air, another mixture of gases, or pureoxygen), that is coupleable to the multi-lumen barrier, and oxygen isactively supplied to the islets in the barrier by the source of oxygen.In such applications, the multi-lumen barrier is disposed within ahousing, e.g., a scaffold, and the source of oxygen is coupleable to thehousing. For some applications of the present invention, the multi-layerimmune barrier is implanted in a well-perfused area of the body of therecipient in order to allow for sufficient oxygen to flow toward theislets that are encapsulated within the multi-layer immune barrier. Forsome applications of the present invention, the multi-layer immunebarrier is implanted subcutaneously. The multi-layer immune barrier maybe implanted independently of the source of oxygen.

There is therefore provided, in accordance with some applications of thepresent invention apparatus, including:

a plurality of donor cells;

a first alginate structure that encapsulates the plurality of donorcells, the first alginate structure having a guluronic acidconcentration of between 64% and 74%;

a second alginate structure that surrounds the first alginate structure,the second alginate structure having a mannuronic acid concentration ofbetween 52% and 60%; and

a selectively-permeable membrane coupled at least in part to the secondalginate structure.

In some applications of the present invention, the selectively-permeablemembrane surrounds the second alginate structure.

In some applications of the present invention, the selectively-permeablemembrane is embedded at least in part within the second alginatestructure.

In some applications of the present invention, the guluronic acidconcentration of the first alginate structure is between 67% and 71%.

In some applications of the present invention, the mannuronic acidconcentration of the second alginate structure is between 54% and 58%.

In some applications of the present invention, the plurality of donorcells include cells of pancreatic islets.

In some applications of the present invention, the first alginatestructure has a thickness of 300-700 um.

In some applications of the present invention, the first alginatestructure has a thickness of 400-700 um.

In some applications of the present invention, the first alginatestructure has a thickness of 500 um.

In some applications of the present invention, the first alginatestructure has a thickness of 600 um.

In some applications of the present invention, the first alginatestructure has a dry matter content of at least 1.8%.

In some applications of the present invention, the first alginatestructure has a dry matter content of at least 2.2%.

In some applications of the present invention, the first alginatestructure has a dry matter content of between 1.8 and 4.2%.

In some applications of the present invention, the dry matter content ofthe first alginate structure is between 2.2 and 4.0%.

In some applications of the present invention, the first alginatestructure has a dry matter content of between 1.8 and 3.0%.

In some applications of the present invention, the dry matter content ofthe first alginate structure is between 2.2 and 2.6%.

In some applications of the present invention, the second alginatestructure has a dry matter content of between 3.0 and 7.0%.

In some applications of the present invention, the dry matter content ofthe second alginate structure is between 5.5 and 6.5%.

In some applications of the present invention, the second alginatestructure has a dry matter content of between 3.0 and 5.0%.

In some applications of the present invention, the dry matter content ofthe second alginate structure is between 3.5 and 4.5%. In someapplications of the present invention, the plurality of donor cellsinclude cells that are disposed in a plurality of pancreatic islets, andthe first alginate structure encapsulates that plurality of pancreaticislets at a density of between 1000 and 6500 islet equivalents (IEQ) persquare cm.

In some applications of the present invention, the plurality of donorcells include cells that are disposed in a plurality of pancreaticislets, and the first alginate structure encapsulates that plurality ofpancreatic islets at a density of between 1500 and 6000 islets persquare cm.

In some applications of the present invention, the first alginatestructure encapsulates that plurality of pancreatic islets at a densityof between 3500 and 4500 islets per square cm.

In some applications of the present invention, the second alginatestructure has an inner surface that is in contact with an outer surfaceof the first alginate structure, the apparatus has an external surfacethat is not in contact with the first alginate structure, and a distancebetween the inner surface of the second alginate structure and theexternal surface of the apparatus is between 25 um and 50 um.

In some applications of the present invention, the membrane is embeddedwithin the second alginate structure, and the second alginate structurehas an outer surface thereof which defines the external surface of theapparatus.

In some applications of the present invention, a distance from anexternal surface of the apparatus to a center of the first alginatestructure is 300-500 um.

In some applications of the present invention, the distance from theexternal surface of the apparatus to the center of the first alginatestructure is 350 um.

In some applications of the present invention, the distance from theexternal surface of the apparatus to the center of the first alginatestructure is 300 um.

In some applications of the present invention, the membrane is embeddedwithin the second alginate structure, and the second alginate structurehas an outer surface thereof which defines the external surface of theapparatus.

In some applications of the present invention, the selectively-permeablemembrane has a pore size of up to 0.2 um.

There is additionally provided, in accordance with some applications ofthe present invention, a method for encapsulating a plurality of donorcells, including:

encapsulating the plurality of donor cells in a first alginate structurehaving a guluronic acid concentration of between 64% and 74%;

surrounding the first alginate structure by a second alginate structurehaving a mannuronic acid concentration of between 52% and 60%; andsurrounding the second alginate structure by a selectively-permeablemembrane.

In some applications of the present invention, the guluronic acidconcentration of the first alginate structure is between 67% and 71%,and surrounding the plurality of donor cells in the first alginatestructure includes surrounding the plurality of cells in the firstalginate structure having the guluronic acid concentration of between67% and 71%.

In some applications of the present invention, the mannuronic acidconcentration of the second alginate structure is between 54% and 58%,and surrounding the first alginate structure by the second alginatestructure includes surrounding the first alginate structure by thesecond alginate structure having the mannuronic acid concentration ofbetween 54% and 58%.

In some applications of the present invention, the plurality of donorcells include cells that are disposed in a plurality of pancreaticislets, and encapsulating the plurality of donor cells in the firstalginate structure includes encapsulating the plurality of pancreaticislets in the first alginate structure at a density of between 1000 and6500 islet equivalents (IEQ) per square cm.

In some applications of the present invention, the plurality of donorcells include cells that are disposed in a plurality of pancreaticislets, and encapsulating the plurality of donor cells in the firstalginate structure includes encapsulating the plurality of pancreaticislets in the first alginate structure at a density of between 1500 and6000 islets per square cm.

In some applications of the present invention, encapsulating theplurality of pancreatic islets in the first alginate structure includesencapsulating the plurality of pancreatic islets in the first alginatestructure at a density of between 3500 and 4500 islets per square cm.

There is also provided, in accordance with some applications of thepresent invention, apparatus, including:

a plurality of donor cells;

a first alginate structure that encapsulates the plurality of donorcells, the first alginate structure having a distance from an outersurface thereof to a center of the first alginate structure, thedistance being configured so as to attenuate diffusion toward theplurality of donor cells of molecules;

a second alginate structure that surrounds the first alginate structure,the second alginate structure having a structural composition selectedso as to restrict passage therethrough of molecules having a molecularweight above and including 150 kDa; and

a selectively-permeable membrane coupled at least in part to the secondalginate structure, the membrane being configured to restrict passagetherethrough of cells.

In some applications of the present invention, the first alginatestructure is configured so as to attenuate diffusion toward theplurality of donor cells of negatively-charged molecules.

In some applications of the present invention, the second alginatestructure has an inner surface that is in contact with an outer surfaceof the first alginate structure, the apparatus has an external surfacethat is not in contact with the first alginate structure, and a distancebetween the inner surface of the second alginate structure and theexternal surface of the apparatus is between 25 um and 50 um.

In some applications of the present invention, the membrane is embeddedwithin the second alginate structure, and the second alginate structurehas an outer surface thereof which defines the external surface of theapparatus.

In some applications of the present invention, the membrane is embeddedwithin the second alginate structure, and the second alginate structurehas an outer surface thereof which defines the external surface of theapparatus.

The present invention will be more fully understood from the followingdetailed description of applications thereof, taken together with thedrawing, in which:

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic illustration of a multi-layer immune barrierhaving an inner first alginate structure that encapsulates a pluralityof donor cells, in accordance with some applications of the presentinvention;

FIG. 2 is a schematic illustration of a plurality of multi-layer immunebarriers coupled to a housing, in accordance with some applications ofthe present invention;

FIG. 3 is a schematic illustration of the housing of FIG. 2 couplable toa source of oxygen, in accordance with some applications of the presentinvention; and

FIG. 4 is a schematic illustration of a subcutaneously-implantablehousing for holding one or more multi-layer immune barriers, inaccordance with some other applications of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference is now made to FIG. 1, which is a schematic illustration of asystem 20 comprising a multi-layer immune barrier 22, in accordance withsome applications of the present invention. Multi-layer immune barrier22 comprises a first, inner alginate hydrogel layer 26 whichencapsulates a plurality of donor cells and/or tissue 24.

Typically, cells and/or tissue 24 comprise a plurality of islets ofLangerhans. First, inner alginate layer has a guluronic acidconcentration of between 64% and 74%, e.g., between 67% and 71%.Multi-layer immune barrier 22 further comprises a second, outer alginatestructure 28 that surrounds at least in part (e.g., entirely, as shown)first, inner alginate structure 26. Second alginate structure has amannuronic acid concentration of between 52% and 60%, e.g., between 54%and 58%.

For some applications, first alginate structure 26 has a dry mattercontent of at least 1.8%, e.g., at least 2.2%. For example, the firstalginate structure may have a dry matter content of between 1.8 and4.2%, such as between 2.2 and 4.0%.

For some applications, first alginate structure 26 has a dry mattercontent of between 1.8 and 3.0%, e.g., typically between 2.2 and 2.6%.First alginate structure 26 is typically cross-linked with a divalentcation, e.g., Strontium. Typically, second alginate structure 28 has adry matter content of between 3.0 and 7.0%, e.g., between 5.5 and 6.5%.For some applications, second alginate structure 28 has a dry mattercontent of between 3.0 and 5.0%, e.g., typically between 3.5 and 4.5%and is crossed-linked with a divalent cation, e.g., Barium.

Typically, at least one semi-permeable membrane 30 is coupled to second,outer alginate structure 28 of barrier 22. Typically, membrane 30comprises a Biopore™ membrane of approximately 25 um thickness. Membrane30 may comprise silicone or hydrophilized Teflon, by way of illustrationand not limitation. Membrane 30 reduces fibrosis and furtherimmunoisolates the islets encapsulated in first alginate structure 26.Typically, the Biopore™ membrane 30 is embedded, or integrated withinthe alginate of second, outer alginate structure 28. For someapplications of the present invention two or more membranes 30 (e.g.,Biopore™, a Teflon™ membrane, or equivalent having a pore size of 0.25um each) are impregnated within one or more alginate structures 28.Membrane 30 has a width of between 25 and 75 um. The two of moremembranes/alginate structure(s) are placed one on top of the other tofurther restrict passage of constituents therethrough. Typically, asdescribed hereinbelow, a plurality of first alginate structure 26 aredisposed within an implantable housing, and second alginate structure 28are coupled to a cover which covers the housing.

High-M alginate of second-outer alginate structure 28 is layered oneither side of membrane 30. The alginate hydrogel of second, outeralginate structure is cross-linked by immersing the membrane-alginatesystem in 20-60 mM Barium chloride solution (e.g., typically 30 mM) fora period of 5-60 min (e.g., typically 12-16 min). As a result, second,outer alginate layer 28 comprises a membrane-alginate layer, whereinmembrane 30 comprises a physical porous membrane in which the pores ofmembrane 30 are filled with cross-linked, high M, alginate.

Membrane 30 has a thickness of up to 25 um and a pore size of up to 0.5um, e.g., 0.2 um. As described hereinabove, one or more membranes 30 isincorporated, embedded, or disposed within second, outer alginatestructure 28. For other applications, membrane 30 surrounds secondalginate structure 28 at an outer surface thereof.

The primary role of membrane 30 of multi-layer immune barrier 22 is toprevent cell-cell contact between donor cells 24 contained within first,inner alginate structure 26 and host cytotoxic T-cells. Thus, a directeffect of killing of donor cells 24 by the host cytotoxic cells isprevented.

Second, outer alginate structure 28 that surrounds first alginatestructure 26 comprises a relatively high percentage mannuronic acid andis typically cross-linked with

Barium. For some applications, second alginate structure 28 iscross-linked with Strontium or with Calcium. Additionally, secondalginate structure 28 has a dry matter content of at least 3%. Takingtogether the properties of second alginate structure 28 (i.e., the highmannuronic acid concentration, the cross-linking of the alginate withBarium, and the increased dry matter concentration), it is hypothesizedby the inventors that second alginate structure 28 significantly reducesthe diffusion rates of macromolecules and large proteins, e.g.,immunoglobulins and complement members, and their ability to passthrough toward the islets that are encapsulated in first, inner alginatestructure 26. Typically, these macromolecules have molecular weightstructures which range between 150 kDa and 1500 kDa, e.g., between 150kDa and 900 kDa. For example, second alginate structure restrictspassage toward cells 24 of IgG having a molecular weight ofapproximately 150 kDa, a complement member having a molecular weight ofup to 400 kDa, and of IgM which has a molecular weight of over 750 kDa.

Typically, second alginate structure 28 attenuates inward diffusion ofimmunoglobulin IgG (150 kDa), complement members C3 and C5 (190 kDaEach) and prevents the diffusion of complement C1 (400 kDa) and IgM (750kDa), thereby prevents damage to cells associated with activation of thecomplement system.

The permeability properties of second alginate structure 28 weredetermined by considering the size, molecular weight, shape, and chargeof the proteins that are designated to be restricted by second alginatestructure 28. That is, second alginate structure 28 defines a pore sizeof 18 nm or lower. Additionally, second alginate structure 28 provides(a) obstructions which increase the path length for diffusion ofmolecules and polymer chains thorough the alginate, and (b) residual,polar, and hydrophobic charges which interact with the molecules andpolymer chains diffusing through the alginate.

Alternatively, second alginate structure 28 comprises a medium guluronicacid concentration of between 47-57% and short G-blocks (i.e., chains ofguluronic acid comprising fewer than 15 consecutive guluronic acidresidues).

For either application in which second alginate structure 28 comprises ahigh mannuronic acid concentration or a medium guluronic acidconcentration, as described hereinabove, second alginate structure 28imparts biocompatibility to multi-layer immune barrier 22 because itreduces the innate immune response of inflammatory cells which aretypically attracted to alginates having a high percentage of guluronicacid concentration (i.e., a high G-content). Therefore, it ishypothesized by the inventors that by increasing the percentage ofmannuronic acid and/or by reducing the percentage of guluronic acidconcentration of second alginate structure 28 (i.e., the alginatestructure adjacent an external surface 29 of multi-layer immune barrier22), the innate immune response against multi-layer immune barrier 22 isreduced. Additionally, membrane 30 prevents passage of immune cells(e.g., macrophages, neutrophils, antigen presenting cells, etc.) of therecipient through second alginate structure 28 and thereby through firstalginate structure 26.

Under physiological conditions, the alginates of second alginatestructure 28 and first alginate structure 26 are negatively charged.Additionally, under physiological conditions (e.g., physiological pH),most proteins are also negatively charged. Therefore, (a) in response tocharge-charge interaction between the alginate and the proteins (e.g.,chemokines and cytokines like IL-1 beta, TNF alpha, and interferongamma) of the recipient, the inward diffusion through the alginate ofproteins of the recipient will be attenuated, and in some cases,substantially eliminated, while (b) outward diffusion of proteins, e.g.,insulin, from the encapsulated islets will be accelerated.

In such a manner, multi-layer immune barrier 22 functions as a membraneto immunoisolate the transplanted islets, and thus, the recipient mammaldoes not need to undergo immunosuppression (e.g., via administration ofa drug) prior to and following implantation. Additionally, theelectrical attraction/repulsion of the particles passing through thealginate supplements the immunoisolation properties of the alginateslab.

As described hereinabove, multi-layer immune barrier 22 has an externalsurface 29 thereof. For application in which membrane 30 is embeddedwithin second alginate structure 28, an outer surface of second alginatestructure 28 defines external surface 29 of multi-layer immune barrier22. Second alginate structure 28 surrounds first alginate structure 26in a manner in which multi-layer immune barrier 22 has a thickness orwidth W2 of between 30 um and 60 um, e.g., 50 um, between externalsurface 29 of multi-layer immune barrier 22 and inner surface 27 ofsecond alginate structure 28.

Typically, surface 29 is generally smooth.

First alginate structure 26 has an outer surface 25 thereof that is incontact with inner surface 27 of second, outer alginate structure 28.

It is to be noted that the scope of the present invention includes theplacement of membrane 30 between outer surface 25 of first alginatestructure 26 and inner surface 27 of second, outer alginate structure28.

Reference is now made to FIGS. 2 and 3, which are schematicillustrations of a subcutaneously-implantable device 180 comprising ahousing 120 which supports one or more multi-lumen barriers 22, inaccordance with some applications of the present invention. Typically,housing 120 is configured for implantation in an animal that isnon-human, e.g., a pig. Housing 120 comprises an upper housing element130 a and a lower housing element 130 b. Upper and lower housingelements 130 a and 130 b comprise a biocompatible material (e.g.,polyether ether ketone (PEEK)). Each housing element 130 a and 130 b areshaped to define a plurality of wells which each support a respectiveone of a plurality of first alginate structures 26 which hold theplurality of islets.

Housing 120 is coupled to one or more (e.g., a plurality)oxygen-delivering tubes 170 which facilitate provision of oxygen to theislets in alginate structures 26 within housing 120. Tubes 170 are influid communication with an oxygen reservoir which is surrounded by areservoir housing having an upper oxygen reservoir housing element 132 aand a lower oxygen reservoir housing element 132 b which provide a spacefor oxygen to be stored from tubes 170. Oxygen reservoir housingelements 132 a and 132 b are each shaped so as to define a plurality ofholes 134 for passage of oxygen therethrough and toward first alginatestructures 26 which hold the islets. Oxygen reservoir housing elements132 a and 132 b comprise plastic which is covered with silicone toregulate the oxygen provision. Housing 120 facilitates housing andprovision of oxygen in a concentration of between 40% and 95% e.g., 95%,at a pressure of between 1 atm and 2 atm, (e.g. 1.35 atm), on a dailybasis.

Housing 120 also comprises an upper cap 140 a and a lower cap 140 bwhich are coupled to upper and lower housing elements 130 a and 130 b,respectively. Each cap 140 a and 140 b is coupled to (e.g., glued to)one or more second alginate structures 28 (which each contain arespective membrane 30, as described hereinabove). Each second alginatestructure 28 is aligned with a respective first alginate structure 26.Typically, first alginate structures 26 are assembled upon a metalscaffold, as shown in the image of lower cap 140 b. Taken together,first alginate structures 26 and the respective second alginatestructure 28 aligned therewith, form respective multi-layer immunebarriers 22, as shown in the image of lower cap 140 b.

As shown in FIG. 2, housing 120 holds fourteen multi-lumen immunebarriers 22. It is to be noted that housing 120 may hold any number ofbarriers 22, e.g., between 1 and 20 barriers. The islets (shown as cellsand/or tissue 24) encapsulated within first alginate structure 26 aretypically disposed within a center of first alginate structure 26. Eachone of the plurality of first alginate structures 26 is configured so asto encapsulate between 1500 and 6000 islets per square cm, e.g.,typically, between 3500 and 4500 islets, and has an area ofapproximately 1 cm̂2, by way of illustration and not limitation. For someapplications, each one of the plurality of first alginate structures 26is configured so as to encapsulate between 1000 and 6500 isletequivalents (IEQ) per square cm. First alginate structure 26 has athickness, or width W1 of between 300 um and 700 um, e.g., between 400um and 700 um, e.g., 500 um or 600 um. Multi-layer immune barrier 22 istypically coin- or disc-shaped. Typically, the first alginate structure26 has a total surface area of 1 cm̂2.

That is, for embodiments in which housing 120 comprises 14 slabs, asshown (e.g., for embodiments in which housing 120 is implanted in a pigor a human), housing 120 contains a total density of between 21,000 and84,000 islets/cm̂2, e.g., 28,000 islets/cm̂2.

Reference is now made to FIG. 4, which is a schematic illustration of asubcutaneously-implantable device 200 comprising a housing 220 whichsupports one or more multi-lumen barriers 22, in accordance with someapplications of the present invention. Typically, housing 220 isconfigured for implantation in human and is identical to housing 120, asdescribed herein, with the exceptions as described herein. Housing 220facilitates implantation of islets at a higher density than housing 120.Housing 220 holds a total density of up to 450,000 islets/cm̂2 eachalginate structure 26 is disposed in one or more slabs at upper housingelement 130 a and lower housing element 130 b. Each slab has a surfacearea of approximately 100 cm̂2 and holds islets at a density of 3000-6000e.g., 4500 islets/cm̂2. For some applications of the present invention,each housing element 130 a and 130 b holds one slab barrier 22 that isdivided into one or more subcomponents 222 (e.g., a plurality, as shown)each having a surface area of between 1 and 100 cm̂2.

It is to be noted that FIG. 4 shows only upper housing element 130 a andupper cap 140 a for clarity of illustration, and that the bottom half ofhousing 200 is identical to the upper half of housing 220, as shown anddescribed herein.

Reference is now made to FIGS. 2-4. For applications in which housing120 is configured for implantation in a pig (FIGS. 2-3), housing 120 hasa height of 15-20 mm (e.g., 17 mm), and an outer diameter of 60-70 mm(e.g., 68 mm). For applications in which housing 220 is configured forimplantation in a human (FIG. 4), housing 220 has a height of 15-40 mm(e.g., 25 mm) and an outer diameter of 70-120 mm (e.g., 90 mm).

For some applications, when each immune barrier 22 contains islets at adensity of 3000 islets/cm̂2, a plurality of slab-bearing inserts are usedin order to form barrier 22 into a slab shape.

Typically, first alginate structure 26 encapsulates islet at densitiesranging from 1500 to 6000 per square cm. Each islet has an averagediameter of 124 um and a calculated volume of 1 nl. For example, whenfirst alginate structure 26 encapsulates islets at a density of 3000islets/cm̂2 barrier 22 has a volume density (v/v) of 6% and, thefootprint (that is, the surface are of the islets relative to thesurface area of alginate structure 26) of 36%.

Taking together the dimensions of first alginate structure 26 and secondalginate structure 28, multi-layer immune barrier 22 defines a distanceD1 between external surface 29 thereof and the center of first alginatestructure 26 of between 240 um and 320 um, e.g., between 260 um and 300um. For some applications, the distance from the external surface to thecenter of first alginate structure is 300-500 um, e.g., 300 um-350 um.That is, for embodiments in which the islets are disposed substantiallyin a vicinity of the center of first alginate structure 26, multi-layerimmune barrier 22 provides a relatively large traveling distance formolecules having a very low molecular weight and short half-life (e.g.,reactive oxygen species (ROS), nitric oxide (NO) or H₂O₂). Since amajority of distance D1 is provided by first alginate structure 26,first alginate structure 26 functions to help attenuate and, in somecases, eliminate, the diffusion of these molecules toward theencapsulated islets.

Nitric oxide (NO) is a short-living molecule having a life-span ofapproximately 2-4 seconds and can travel only short distances away fromits site of synthesis. The effective travelling distance of NO isdefined as the distance within which its concentration is greater thanthe equilibrium dissociation constant of its target enzyme (guanylylcyclase). This distance is estimated at 100-250 um. Taking intoconsideration that NO is produced by neutrophils and macrophages,multi-layer immune barrier 22 provides a defense strategy against NO byincreasing the effective distance between these cells and the donorislets encapsulated within first alginate structure 26. Firstly, thisdistance is increased by (1) minimizing adhesion of inflammatory cellsonto alginate surfaces (i.e., as described hereinabove by reducing theG-content of the alginate adjacent to external surface 29 of multi-layerimmune barrier 22), (2) restricting passage of NO-producing cellsthrough membrane 30, and (3) increasing the diffusion path betweenNO-producing cells and donor islets (i.e., by multi-layer immune barrier22 which defines distance D1 between external surface 29 thereof and thecenter of first alginate structure 26).

Multi-layer immune barrier 22 restricts passage of cytokinesresponsively to the electrostatic repulsion forces of alginatestructures 26 and 28. Width W1 of first alginate structure 26 (FIG. 1)provides a larger area for electrostatic forces to act upon thecytokines as they diffuse through first alginate structure 26.

Additionally, since first alginate structure 26 has a relatively highguluronic acid concentration, first alginate structure 26 impartsflexibility to multi-layer immune barrier 22.

FIG. 3 shows subcutaneously-implantable device 180 coupled to ports 172which facilitate active provision of oxygen to cells and/or tissue 24disposed within multi-layer barrier 22, in accordance with someapplications of the present invention. As shown, housing 120 supportsone or more (e.g., a plurality of) multi-layer immune barriers 22.Housing 120 is coupled to a plurality of fluid-injection ports 172.Ports 172 are disposed remotely from housing 120 and are coupled theretoby respective tubes 170 (tubes 170 are coupled to housing 120 as showneither in FIG. 2 or 3). The remote positioning of ports 172 with respectto housing 120 facilitates the delivery of fluid to housing 120 withoutsubstantially shifting the position of housing 120. An upper surface ofeach port comprises a penetrable surface 128, which functions as anoxygen delivery interface 127. Tube 170 facilitates transfer of oxygenfrom ports 172 to an oxygen reservoir 42 within housing 120 and towardmulti-layer immune barriers 22 encapsulating the islets.

As shown, a user 21 grips a portion of skin 126 that lies over one ofports 172. The user penetrates penetrable surface 128, typically with aneedle. A source of oxygen (not shown), e.g., a vessel such as asyringe, comprising a source of fluid which comprises oxygen, is coupledto the needle and supplies via the needle fluid containing oxygen to theislets that are disposed within multi-lumen barriers 22. In someapplications of the present invention, the source of oxygen comprisesair. Alternatively, the source of oxygen comprises pure oxygen.

In some applications of the present invention, the source of oxygencomprises a plurality of gases including oxygen. The gases are disposedin the container at a pressure of 1 atm or higher (e.g., 1.35 atm).Typically, the source of oxygen comprises around 5% carbon dioxide inorder to maintain a balance of concentrations of carbon dioxide insidethe housing and outside the housing. For some applications, the sourceof oxygen comprises a fluid comprising oxygen carriers (e.g.,hemoglobin-based oxygen carriers such as chemically-modified hemoglobin,or “microbubbles” which comprise fluorocarbons such asdodecafluoropentane or perfluorodecalin) that are loaded with oxygenprior to the injection of the carriers into housing 120. The carriersfacilitate the transport into housing 120 of a larger volume ofcompressed oxygen.

Oxygen reservoir housing 132 defines a space having a volume of between75 ml and 300 ml, e.g., between 100 ml and 150 ml. Oxygen reservoirhousing 132 comprises foam, e.g., an open-cell silicone foam, or simplyan air gap which functions as a gas reservoir within the device.Reservoir 42 functions as a conduit for oxygen diffusion to thefunctional cells, as well as a reservoir for storing excess oxygen thatis supplied to the housing by the source of oxygen. Techniques describedherein with respect to oxygen reservoir housing 132 may be practiced incombination with techniques described with respect to an air gap in PCTPatent Application PCT/IL08/001204 to Stern et al., which isincorporated herein by reference.

In some applications of the present invention, housing 120 comprises theoxygen carriers. In such applications, the oxygen carriers function tostore, or carry, oxygen when in excess, and release the oxygen upon aneed therefore.

As shown in the enlarged cross-sectional image, each multi-layer immunebarrier is coupled to two layers of second alginate structure 28,wherein a respective membrane 30 is embedded within each alginatestructure 28. It is to be noted that any number of alginate structures28 and membranes 30 may be used.

A respective gas-permeable membrane 150 is disposed between eachalginate structure 26 and housing elements 130 to facilitate passage ofoxygen from oxygen reservoir housing 132 to the islets disposed in eachalginate structure 26 of each multi-lumen barrier 22.

Housing 120 is shown as being disc-shaped by way of illustration and notlimitation. For example, housing 120 may be rectangular or any othersuitable shape suitable for implantation under skin 126 of therecipient. In some embodiments, housing 120 is shaped to provide aplurality of projections which project radially from housing 120 andtoward a vicinity of the body of the recipient which includesvasculature. In such applications, the projections function as oxygendelivery interface 127 by providing increased surface area of housing120 for facilitating transport of oxygen from surrounding vasculaturetoward housing 120. For some applications, the projections of housing120 contain the oxygen carriers, which store excess oxygen that has beenabsorbed into housing 120 by the projections.

At some time following implantation of housing 120 in the body of therecipient, housing 120 is primed with a suitable amount ofoxygen-containing fluid. (The housing may have previously been filledwith oxygen-containing fluid, as well.)

Techniques for active oxygen provision may be practiced together withany one of the techniques described in U.S. patent application Ser. No.12/315,102 to Stern et al., entitled, “Apparatus for transportation ofoxygen to implanted cells,” filed on Nov. 26, 2008, which isincorporated herein by reference.

The scope of the present invention includes the encapsulation of cellsand/or tissue 24 in multi-layer immune barrier 22 other than theplurality of islets, as described herein. That is, cells and/or tissue24 which are encapsulated in multi-layer immune barrier 22 include cellsfound in pancreatic islets (e.g., beta cells, alpha cells, otherpancreatic islet cells), hepatic cells, hepatocytes, neural andneuroendocrine cells, renal cortex cells, vascular endothelial cells,thyroid cells, parathyroid cells, adrenal cells (e.g., chromaffincells), thymic cells, adrenal cells, ovarian cells,genetically-engineered cells, cloned cells, stem, cells, and/ortesticular cells.

Additionally, techniques described herein may be performed incombination with techniques described in one or more of the followingpatent application, all of which are incorporated herein by reference:

US Patent Application Publication 2004/0133188 to Vardi et al.,entitled, “Implantable device,” filed Mar. 12, 2004;

US Patent Application Publication 2005/0136092 to Rotem et al.,entitled, “Implantable device,” filed Nov. 30, 2004;

US Patent Application Publication 2009/0012502 to Rotem et al.,entitled, “Oxygen supply for cell transplant and vascularization,” filedJun. 4, 2008;

PCT Publication WO 09/031154 to Stern and Rozy, entitled, “Air gap forsupport cells,” filed Sep. 7, 2008;

US Patent Application Publication 2010/0047311 to Rotem et al.,entitled, “Protecting algae from body fluids,” filed Jul. 31, 2009;

PCT Publication WO 10/032242 to Barkai et al., entitled, “Optimizationof alginate encapsulation,” filed Sep. 16, 2009; and/or

PCT Publication WO 10/061387 to Stern et al., entitled, “Apparatus fortransportation of oxygen to implanted cells,” filed Nov. 25, 2009.

For some applications of the present invention, techniques describedherein are practiced in combination with techniques described in one ormore of the references cited in the Background or Cross-referencessections of the present patent application.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

1. A method for encapsulating a plurality of donor cells, comprising:encapsulating the plurality of donor cells in a first alginate structurehaving a guluronic acid concentration of between 64% and 74%;surrounding the first alginate structure by a second alginate structurehaving a mannuronic acid concentration of between 52% and 60%; andsurrounding the second alginate structure by a selectively-permeablemembrane.
 2. The method according to claim 1, wherein the guluronic acidconcentration of the first alginate structure is between 67% and 71%,and wherein surrounding the plurality of donor cells in the firstalginate structure comprises surrounding the plurality of cells in thefirst alginate structure having the guluronic acid concentration ofbetween 67% and 71%.
 3. The method according to claim 1, wherein themannuronic acid concentration of the second alginate structure isbetween 54% and 58%, and wherein surrounding the first alginatestructure by the second alginate structure comprises surrounding thefirst alginate structure by the second alginate structure having themannuronic acid concentration of between 54% and 58%.
 4. The methodaccording to claim 1, wherein the plurality of donor cells include cellsthat are disposed in a plurality of pancreatic islets, and whereinencapsulating the plurality of donor cells in the first alginatestructure comprises encapsulating the plurality of pancreatic islets inthe first alginate structure at a density of between 1000 and 6500 isletequivalents (IEQ) per square cm.
 5. The method according to 1, whereinthe plurality of donor cells include cells that are disposed in aplurality of pancreatic islets, and wherein encapsulating the pluralityof donor cells in the first alginate structure comprises encapsulatingthe plurality of pancreatic islets in the first alginate structure at adensity of between 1500 and 6000 islets per square cm.
 6. The methodaccording to claim 5, wherein encapsulating the plurality of pancreaticislets in the first alginate structure comprises encapsulating theplurality of pancreatic islets in the first alginate structure at adensity of between 3500 and 4500 islets per square cm.